Turbochargers are generally used to enhance operability of a device. For example, in the context of turbine engines, turbochargers may be used to heat a volumetric flow of engine exhaust gas to pressurize or boost an intake air stream into a combustion chamber. In this regard, exhaust gas from the engine may be routed into a turbocharger turbine housing within which a turbine is mounted. The exhaust gas flow impinges against the turbine to cause it to spin. Because the turbine is mounted on one end of a shaft that has a radial air compressor mounted on an opposite end, rotary action of the turbine also causes the air compressor to spin. The spinning action of the air compressor causes intake air to enter a compressor housing and to be pressurized or boosted before the intake air is mixed with fuel and combusted within an engine combustion chamber.
To reduce friction between and to extend the useful lives of the rotating components of the turbocharger, foil bearings may be used to support rotating components of the turbine engines, turbochargers, and the like. Generally, a foil bearing includes a journal mounted to the rotating component and a cylindrical top foil disposed around the journal. The journal and top foil are configured such that when the rotating component rotates at an optimum operational speed, the foil and the journal separate from each other to form an air gap. As the air gap between the foil and the journal grows, pressurized air is drawn in to serve as a load support and act as a lubricant to the rotating component and surrounding static components.
In the absence of the pressurized air between the journal and the top foil, the two components may come into contact with each other or with other surrounding components. Thus, to protect the components from premature wear, one or more of the components may include a solid lubricant coating thereon. Some known solid lubricants include graphite fluoride/polymer composites and molybdenum disulfide. However, these materials may not be particularly useful for high temperature machinery since they are only stable at temperatures below about 250° C. Other known solid lubricants include silver, calcium fluoride, and barium fluoride, but these materials may not perform adequately in some circumstances because they may have relatively high porosity and may be relatively difficult to coat. Ternary carbide and nitride materials have also been used as solid lubricants. However, the application process may at least partially decompose the materials, and as a result, the properties of the material may not be fully optimized when used as coatings on components that are exposed to high turbocharger operating temperatures (e.g., temperatures above 535° C.)
Hence, there is a need for methods for manufacturing and/or coating turbocharger components, where the properties of the materials within the resultant coating, such as the low friction coefficient and low wear rate properties of the coating, are optimized when tribocoupled with superalloy materials. Additionally, there is a need for a coating that has improved oxidation-resistance, as compared to conventional coatings. Moreover, it is desirable for the methods of manufacturing the coating to be relatively simple and inexpensive to perform.